Still more evidence that vaccines don’t cause autism

The mercury militia and MMR scaremongers aren’t going to like this, not one bit.

What should greet my in box upon my arrival at work after a long Fourth of July weekend, but an alert of a new study of a large population of children in Canada that utterly failed to find an epidemiological link between thimerosal or MMR vaccination and autistic spectrum disorders. It’s the latest in a continuous line of epidemiological studies and, to my knowledge, the most comprehensive epidemiological study to look at exposure to both MMR and thimerosal-containing vaccines. (The MMR vaccine, being a live virus vaccine, does not contain thimerosal and has never contained thimerosal.) In and of itself it represents strong, albeit not conclusive evidence that vaccines do not cause autism, but when coupled with various other studies, it represents yet another nail in both the hypothesis that the mercury in thimerosal in vaccines causes autism and the hypothesis that the MMR vaccine somehow causes autism. I predict an attack coming. Actually, the attack has already come (as I will discuss below), but I’m sure more will follow from the mercury militia and antivaccination crowd in the coming days.
Published by Eric Fombonne at McGill University in Montreal, this study examined 27,749 children born from 1987 to 1998 attending 55 different schools. Cumulative thimerosal exposure was by age 2 years was calculated for the 1987-1998 birth cohorts. This exposure ranged from 100-125 Î¼g from 1987 to 1991, 200-225 Î¼g from 1992 to 1995, and then none after 1996, which was when thimerosal was completely removed from vaccines in Canada. Moreover, it was able to compare a period of time when only one MMR immunization (pre-1996) at age 12 months to a later period (1996-1998), when a second dose of the MMR vaccine was given at 18 months.

The study surveyed school special needs records for these children for diagnoses of pervasive developmental disorders (PDDs), which includes autism, Asperger’s disease, and autism-spectrum disorders, childhood disintegrative disorder, and PDD not otherwise specified. Patient anonymity was protected, and the authors note that 86% of the cases of PDD identified were diagnosed at Montreal Children’s Hospital, the home institution of the investigators. Prevalence estimates from this data were noted to be increasing steadily throughout the study period. Of note, PDDs continued to rise at the same rate after the discontinuation of thimerosal in vaccines in 1996 as they did before 1996. Multiple statistical analyses were carried out to look for any correlation between thimerosal exposure and PDD prevalence, using thimerosal exposure as a continuous variable and thimerosal in low, medium, and no exposure groups. They redefined their time points and looked to see if that changed their finding of no correlation between thimerosal and PDDs. In order to rule out diagnostic misclassification, which is more common with ASDs and Asperger’s disease than with autism, they even repeated the analysis only for children with autism. They even went back and took into account the increase in thimerosal exposure during two years when a mass vaccination program was undertaken in the wake of an outbreak of meningococcal disease.

And found no correlation yet again between autism prevalence and thimerosal exposure in vaccines. Because the study is from Quebec, I can’t help but say: Quelle surprise! They concluded:

The results were robust and held true when various analyses were conducted to evaluate the potential impact of misclassification on exposure and diagnosis. Within each period of medium, high, or nil exposure, the same trend toward a steady increase in PDD rate was observed, demonstrating total independence of the 2 variables. Our results are entirely consistent with cohort,30-33 case-control,64 and other ecological studies performed in Denmark and Sweden.

They also noted:

…exposure to ethylmercury in some birth cohorts of our study reached levels as high as those that were attained in the US immunization schedule in the 1990s and were higher than those ever reached in the United Kingdom and Scandinavian populations. Thus, the lack of association between PDD rate and high thimerosal exposure found in our study provides new evidence on the absence of an association between autism/PDD and high exposure levels to ethylmercury that is relevant to the North American public.

The investigators performed a similar analysis with MMR vaccine. Because MMR vaccination coverage was and is high in Canada, this analysis was somewhat more difficult to do. However, to make a long story short, performing similar sorts of analyses, the authors found that PDD rates increased every year at the same rate during a time period when MMR coverage rates declined from 96.1% to 92.4% . If MMR were correlated with PDDs, one would expect that at least the rate of increase of autism diagnoses would decrease. It did not, despite multiple statistical analyses.

Overall, it’s a pretty solid study of a large population of children, and its conclusions represent yet more strong evidence suggesting that neither thimerosal nor MMR cause autism or PDDs. I will point out that the evidence in this study seems more solid to me for ruling out an association between autism and thimerosal than it is for autism and MMR, if only because for thimerosal the investigators had the luxury of having a time period during which no thimerosal was included in vaccines to use for comparison.

Not surprisingly, as with Paul Shattuck’s study, it didn’t take long at all for the mercury militia to get the knives out. For example, Safeminds leapt into the fray very quickly. And, equally unsurprisingly, they went for a largely evidence-free ad hominem. First, the non-smearing part of the press release (which is fairly brief):

The study looked at 27,749 students in grades kindergarten through 12th grade in a Montreal school district and found 187 cases of autism.The vast majority of these cases (more than 90%) were born in years in which thimerosal vaccines were widely used for infants in Quebec, as they were in the US. Only a tiny fraction of the autism students were born when thimerosal-free DTP and Hib vaccines were given, and these students may have been exposed to thimerosal from the Hepatitis B vaccine newly recommended for infants of foreign born parents, which made up over one fourth of the greater Montreal population

Actually, the investigators found 180 cases of PDD, which includes autism, ASDs, and PDDs. Geez, it’s right there in the abstract. You don’t even have to read the whole paper. Can’t SafeMinds even actually read and cite correctly? And the statistics took that into account, and, I would point out, the prevalance of PDDs increased each year, which meant that the proportion of children in those later birth cohorts actually had a higher prevalence of autism and PDDs than children in the earlier birth cohorts, the “thimerosal years,” if you will. It’s not clear to me where SafeMinds got their claim that only 10% of the cases came from the no thimerosal time period, the statistical analysis appeared to be appropriate for the methods used. Finally, the mention of Hepatitis B vaccine is just a red herring. Even if SafeMinds’ worst estimate were correct and over 25% of the children born after thimerosal was removed from vaccines received a little bit of thimerosal in a single vaccine, we would still expect to see a decrease in prevalence of PDDs (or, at the very least, a slowing in the rate of increase.) The dose is the poison, after all, and even if 25% were exposed to some thimerosal, that would leave 75% who were not. No such decrease in either PDD prevalence or even the rate of increase of prevalence was observed.

Of course, no SafeMinds “rebuttal” would be complete without an ad hominem attack:

Dr. Fombonne wrongfully claims that large-population studies in the United States, England and Denmark also disprove a link between mercury and autism, and he states that “there is no autism epidemic.” He conveniently ignores the vast body of scientific evidence that has shown that environmental factors such as mercury may have caused the increased number of autism diagnoses in the US and other countries. Dr. Fombonne’s actions have not historically been in the best interest of families with autism–he has declared himself an expert witness on behalf of various pharmaceutical companies in thimerosal-related litigation. Thimerosal is a serious poison that is harmful via inhalation, ingestion or contact with skin. Furthermore, thimerosal-containing vaccines elevate mercury levels in the body to a level where adverse neurological outcomes are known to occur. It is irresponsible for any pediatric doctor to justify injecting our children with mercury.

Note that “environmental factors” usually represent code words for “vaccines.” Either that, or, realizing that the evidence is continuing not to support the claim that mercury in vaccines causes autism, SafeMinds is shifting gears to “environmental factors,” a tactic that is likely to increase in frequency of use as more and more data keeps refuting the thimerosal hypothesis.

In any case, it’s a a bit of a straw man to claim that Dr. Fombonne said that his study “disproves” a link betwee mercury and autism. What Dr. Fombonne did say is that he found no association between vaccines and autism and that his study, as well as the English and Danish studies, do not support the hypothesis that mercury in vaccines causes autism. Note also how Safeminds says that Dr. Fombonne conveniently “ignores evidence” supporting a link between mercury and autism but conveniently excuses itself from mentioning any of it. Then, of course, what mercury militia counterattack would be complete without using the Pharma Shill gambit to try to discredit Dr. Fombonne, as if his receiving support from a pharmaceutical company absolves SafeMinds from having to produce some actual counterevidence to show why Dr. Fombonne is wrong in their estimation. Even if Dr. Fombonne actually worked for a pharmaceutical company as his primary employment, it would not excuse SafeMinds from refuting his results with valid criticisms of his methods and its own counterevidence. Instead, it just repeats the same old data-free mantra that mercury in thimerosal-containing vaccines causes neurologic damage and whine about the “pharma shill” trying to “justify injecting our children with mercury.” One good thing about the “pharma shill” schtick, though: It gives me free rein to point out the numerous and egregious conflicts of interest in, for example, Mark and David Geiers’ funding and research. (Of course, I also explain in excruciating detail why their studies are so poorly designed and don’t show what they claim to show.)

I particularly like the way Kevin Leitch answered this obvious tactic:

And let’s not forget how much money mercury mongers (and chelationists) like Rashid Buttar make using quackery to “remove mercury” from “mercury-poisoned” autistic children and that Mark and David Geier are trying to make by patenting Lupron treatment as a means of “improving the efficacy” of chelation therapy.

The prevalence of all autism spectrum disorders (ASDs) has risen to 1 in 166 children in the past 20 years. Several independent federal agencies and respected scientists and researchers have received federal funds to investigate the autism epidemic and the biological plausibility of a link between mercury and ASDs.

Well, yes they did. So what? The government funds lots of studies on questions that concern the public, and, eight years ago, the mercury hypothesis seemed plausible. Of course, SafeMinds conveniently neglects to mention that nearly all of those well-designed studies funded by federal agencies failed to find any biological or epidemiological evidence for a link between mercury and ASDs.

Multiple studies have indicated that there is a connection between childhood vaccines containing thimerosal and the incidence of autism.

Of course, virtually all of these studies were done by anti-thimerosal activists like Mark and David Geier, and, as I’ve discussed before, are very poorly designed and mine a database for a purpose for which it was never designed.

No conclusions have been made rejecting a link between mercury and autism.

Not exactly. Here, SafeMinds is simply doing what so many other pseudoscientists and cranks do, taking advantage of the natual caution scientists exercise when summarizing their findings. In this case, scientists will often say that the existing well-designed studies do not support a link between mercury and autism, which is true. That doesn’t mean that there isn’t a link, but several very large studies have failed to find it, Even so, it is not strictly correct to say no conclusions have been made rejecting a link between mercury and autism. Conclusions have been made, and those conclusions are that, given the epidemiological and experimental evidence, a link between mercury and autism is not biologically plausible and epidemiologically highly unlikely. Dr. Fombonne’s study is just another one that supports that conclusion. Given all these negative studies, any link, if it exists, must be very weak indeed. Certainly, it isn’t along the lines of Generation Rescue’s oft-repeated claim that “autism and ASDs are misdiagnoses for mercury poisoning.”

In any case, as much as it would be a good thing if this study put the mercury militia’s and antivaccination activists’ scaremongering to rest, it would be naive to think that it will. They are ideologues and unwilling to change their views in response to the science. If even ten years from now, which would be twenty years after thimerosal was removed from Canadian vaccines and thirteen years after it was removed from vaccines in the U.S., autism rates have not fallen dramatically or, as is likely, are flat or still increasing, you can bet that the mercury militia will shift their tactics and claim that environmental mercury is the real cause and that antivaxers will continue to wave their hands and invoke immunological “harm” done by MMR and other vaccines as their real cause.

And children will continue to suffer, as vaccine-preventable diseases make a resurgence, thanks to unjustified fear of vaccines fueled by this hysteria leading to a fall in vaccination rates.

ADDENDUM:Skeptico has more, plus a spot-on comment about the crank technique of insisting that a link hasn’t been ruled out:

Well, proving a universal negative is always difficult, but with one more seemingly well run study finding no link when you would expect to find one if it were there, haven’t we passed the point when it becomes perverse to insist there is a link?

Yes, indeed. I think we passed that point at least a year ago. But that won’t stop SafeMinds and their ilk from insisting that a link “hasn’t been ruled out.” Well, we haven’t completely “ruled out” that homeopathy might “work,” but the preponderance of evidence makes it damned unlikely that it does work or that we will ever find evidence for it. I think we’ve pretty much hit that point with the claim that thimerosal in vaccines causes autism as well.